1. Field of the Invention
The present invention relates to wireless communication systems, and more particularly, to a method for determining when a wireless communication device should rate shift or roam in order to improve communication performance.
2. Description of Related Art
The ability to communicate with people on the move has evolved considerably since Guglielmo Marconi in 1897 first demonstrated radio""s ability to provide continuous contact with ships sailing the English Channel. Since then new wireless communications methods, including mobile radio communications, have grown by orders of magnitude, fueled by electronic miniaturization technologies and the large-scale deployment of affordable, easy-to-use, radio communication networks.
Examples of a radio communication network are a wireless local area network (WLAN) and a wireless wide area network (WWAN). A WLAN comprises a plurality of wireless communication devices that communicate using radio frequency (RF) signals. As in a wired local area network (LAN), the WLAN allows users to seamlessly access disk drives, printers, and additional computer resources and systems connected to the WLAN. The wireless communication devices include a radio receiver/transmitter adapted for RF communication with the other elements of the WLAN. The WLAN may also include a central host processing unit that sends information to and receives information from any one of the plurality of remotely disposed communication devices. The WWAN expands upon the features of the WLAN and offers extended geographic coverage for the communication network that may include a state or even countries.
The central host processor may also form part of a separate wired LAN to provide a bridge with the WLAN. In such a WLAN, the wireless communication devices may comprise portable units that operate within a defined environment to report information back to the central host processing unit. In general, the defined wireless environment may be further divided into basic service areas or cells that are supported by transmitter/receivers of the WLAN for providing segmented but complete wireless coverage for the wireless communication devices over the defined area. The WWAN may incorporate these features of the WLAN or may be a completely wireless network. Thus, WLAN and WWAN systems offer increased flexibility over wired LAN systems by enabling operators of the wireless communication devices substantial freedom of movement through the environment, and are particularly useful for remote communication and data collection applications such as inventory control, manufacturing and production flow management, and asset tracking.
For example, in a WLAN or WWAN, a mobile worker may move throughout the work area carrying a wireless communication device such as a portable terminal or computer. The work area may be within a building or from one building to another and the mobile worker may move from one cell to another. The wireless device must maintain a wireless connection that is transparently maintained so that the central host processing unit and the mobile worker can perform their assigned tasks. As the worker travels within a cell or from one cell to another, it may become necessary for the wireless communication device to lower the transmission rate in order to maintain the connection to the transmitter/receiver of the current cell. Alternatively, the wireless communication device may switch (also known as roam) from the current cell to another cell that may offer better connection quality to the communication network. In either case, the wireless communication device must make this transition without a loss of connection or service degradation being noticed by the mobile worker or the central host processing unit. The transition should be seamless and appear and operate as a wired connection.
In a typical WLAN or WWAN, the wireless communication device determines whether to rate shift or roam based on (1) the failure to successfully transmit and/or (2) comparison of the connection quality between one or more cells with respect to (i) an acceptable predefined threshold or (ii) connection quality. These methods for rate shifting or roaming are relatively inflexible. For example, they cannot be easily modified through configuration parameters or dynamically based on the wireless environment. Furthermore, these methods also react to the state of the wireless connection rather than anticipate the state. By reacting to the state of a connection, the decision to rate shift or roam occurs at the moment when the wireless communication device is ready to transmit. This results in slower response times as conditions change. The wireless network performance suffers and utilization difficulties arise such as delays in transmission, necessary retransmissions, loss of data, or unintelligible voice connections. Finally, there may be a complete connection loss between the wireless communication device and the central host processing unit.
Under some current implementations, delays in rate shifting and/or roaming within a cell or to a new cell may result in the loss of data, voice, or a network connection, such as a TCP/IP network connection, between the wireless communication device and the central host processing unit. When a data or network connection is lost, the worker must reinitiate a logon sequence to the host, then to the required application, and finally repeat the work that was lost. Similarly, when a voice connection is lost, the worker must reestablish the connection, determine at what point in the conversation did the connection fail, and then repeat the conversation for at least the portion that was lost. If the mobile worker is in a location situated at a cell boundary or at the boundary of several cells, the wireless communication device may be unable to effectively maintain a connection due to interference or marginal signal quality. The worker then would be unable to perform the assigned tasks because of the communication connection failure.
This situation can be further aggravated by changing conditions within a cell or among cells of the wireless environment. For example, inventory moved around within a warehouse or workspaces that are reconfigured can affect communication performance, including cell coverage, and place increased demands upon the rate shift and roam functions.
Accordingly, it would be desirable to provide a method for determining when a communication device should rate shift or roam in a wireless environment. The method would improve communication connections and performance by reducing the number of required retransmissions, offer an optimum bandwidth, and faster response time. The method would further reduce network connection losses due to the use of industry standard network protocols by the wireless media. Furthermore, the method would be flexible and anticipate the rate shift and roam requirements, even as the communication environment evolves.
The invention is useful in a method of improving communication performance in a wireless communication system having at least one mobile wireless communication device and a plurality of transmitter/receiver sites that communicate with communication signals, each of which has a geographic area, defined as a cell, within which the at least one mobile wireless communication device can communicate with at least one of the transmitter/receiver sites. In such an environment, according to a first method embodiment of the invention, communication performance is improved by receiving at one of the transmitter/receiver sites the communication signals transmitted by the communication device, and evaluating over time intervals the quality of the communication signals received from the mobile wireless communication device to obtain measurement values of the quality of the evaluated communication signals. A functional relationship value based on the measurement values and a configurable parameter associated with the measurement values are created. The functional relationship value is stored in a memory. An extrapolated functional relationship value based on a stored functional relationship value is calculated, and an optimal one of the plurality of transmitter/receiver sites for communication with the wireless communication device based on the extrapolated functional relationship value is determined.
According to a second method embodiment of the invention, communication performance is improved by receiving at one of the transmitter/receiver sites the communication signals transmitted by the communication device, and evaluating over time intervals the quality of the communication signals received from the mobile wireless communication device to obtain measurement values of the quality of the evaluated communication signals. One of a transmission failure and reception failure of the communication signals is detected. The last measurement value evaluated before the detected one of a transmission failure and a reception failure is stored. A function based on current values of the measurement values and the stored last measurement value is calculated, and whether to make a change in the transmission of the communication signals based at least in part on the function is determined.